RT: Common Lisp regression tester

Everyone knows that it is important to test a system thoroughly
whenever it is changed. However, it is far from easy to come up with
good tests and irritatingly laborious to keep track of a lot of tests
and run them time and again. The RT Common Lisp regression tester
automates part of this task.
Using RT, the programmer still has to come up with tests. However, RT
maintains a database of these tests and automatically runs them when
requested. This can take a lot of computer time, but does not take
any of the programmer's time. As a result, any bugs found by running
the tests---and this is a lot more bugs than you might think---are
essentially found for free.